1. Field of the Invention
An object of the present invention is a method for the automatic adaptation of a light beam emitted by a headlight device, in particular for a motor vehicle. An essential aim of the invention is to automatically optimize, according to the traffic observed on a road, the illumination generated by a vehicle following the road, in particular by offering a light beam, the performance and/or characteristics of which, in terms of range and light intensity, lie between those of the light beams produced by the headlight devices performing a dipped-beam function and those of the light beams produced by headlight devices performing a main-beam function.
2. Description of the Related Art
The field of the invention is, in general terms, that of motor vehicle headlights. In this field, various types of conventional lighting devices are known, among which there are essentially:                sidelights, with low intensity and range;        passing, or dipped-beam lights, with a higher intensity and range on the road of around 60 meters, which are used essentially at night and where the distribution of the light beam is such that it makes it possible not to dazzle the driver of a vehicle being passed;        long-range main-beam lights, whose area of vision on the road is around 200 meters, and which must be switched off when passing another vehicle in order not to dazzle its driver;        fog lights, etc. . . .        
In addition, an improved type of headlight is known, called dual-function headlights, which combine the functions of dipped lights and long-range lights: for this purpose, it is possible for example to arrange inside the dual-function headlight a removable cover, consisting for example of a metal plate, able to move on command from a first position in which it does not obscure the light signal produced by the light source of the headlight, the range of the headlight then corresponding to that of main beams, to a second position in which it obscures part of the light signal produced by the light source of the headlight, the range of the headlight then being limited to that of a dipped light. The headlight must, in the second position, generate a beam with regulatory cutoff corresponding to a beam of the conventional dipped type, the form of the cutoff being given by the form of the shield intercepting part of the light signal. This example embodiment is principally used in headlight devices of the elliptical type.
However, the conventional headlight devices that have just been mentioned, more particularly those that are used as dipped lights, produce light beams that are open to improvement when the headlight devices are used under certain conditions in order to improve the driving comfort.
Thus, when a vehicle is on a motorway, it is judicious to lift the cutoff line compared with that of the beam of a conventional dipped type, and to concentrate the light flux of the dipped light at the optical axis of the headlight device; the beam produced is thus effectively carried a little further. On the contrary, when a vehicle is traveling in the town, it is not necessary to make the light beam carry as far as on a clear road.
Thus, in addition to the conventional principal headlight functions, in particular dipped and main beam, various improvements have progressively appeared. Thus elaborate functions, or advanced functions, have been seen to develop, known by the term AFS functions (standing for Advanced Front light System in English), which slightly modify the positioning of the cutoff of the light beam produced, and possibly its distribution in terms of light intensity, among which there is in particular a function known as Motorway Light in English, meaning motorway light. This function provides an increase in the range of a dipped light, in particular by increasing the light intensity of the beam that it generates at several points in space and by presenting a cutoff line that is raised with respect to that of a conventional dipped beam. In addition, the maximum authorized illumination level changes, in Europe, from 70 lux to 120 lux.
FIG. 1 depicts, by way of example and schematically, three theoretical projections onto a flat surface of various light beams that have just been mentioned. The beams shown correspond to those existing in countries where driving takes place on the right-hand side of the road. The beams corresponding to driving on the left are obtained by simple symmetry. The flat projection surface is disposed facing the headlight device in question, perpendicular to its optical axis. The grey-tinted part of these projections corresponds to an absence of light in the corresponding area in space, the part left white corresponding to an area in space illuminated in a regulatory fashion by means of the headlight device in question.
In this way a first theoretical cutoff line 101 has been shown, corresponding to a dipped beam, a second theoretical cutoff line 102, corresponding to a motorway beam, and a third theoretical cutoff line 103, corresponding to a main beam. The horizon line 104 is shown in broken lines. The theoretical cut-off line of the beam of the dipped type, and respectively of the beam of the motorway type, consists of:                a first part 111, and respectively 121, which takes the form of a first horizontal flat segment disposed below the horizon line 104; in the case of the beam of the dipped type, the projection angle observed between the horizon line and the first segment is −0.57 degrees, while in the case of the beam of the motorway type, the projection angle observed between the horizon line and the first segment is −0.34 degrees;        a second part 112, and respectively 122, which takes the form of a segment inclined by approximately 15 degrees with respect to the horizontal, passing through the horizon line 104;        a third part 113, and respectively 123, which takes the form of a second horizontal flat segment disposed slightly above the horizon line 104.        
Such cutoff lines make it possible not to dazzle the drivers being passed in the opposite direction or followed, by maintaining the cutoff line below the horizon line on the left-hand part of the road, whilst offering a larger area of illuminated space on the right-hand part of the road. Conversely, the cutoff line 103 of the beam of the main-beam type, situated appreciably above the horizon line, causes a dazzling of the driver being followed or passed. This type of function is therefore used only under particular conditions, especially in the absence of vehicles being followed or passed.
The beam of the motorway type therefore corresponds to a beam of the dipped type where the horizontal part of the cutoff line has been raised (on the left of the vehicle for driving on the right) but also where the light intensity has been increased. The motorway function can be fulfilled by means of various types of headlight devices. A first example embodiment lies in the existence of a bender on the previously mentioned cover, acting in the dual-function devices. A bender corresponds to a part of the cover that takes the horizontal position, oriented towards the light source of the headlight device in question, when the cover is positioned so as to intercept part of the light rays produced by the light source. The bender then makes it possible to reflect part of the light rays that would have been intercepted by the cover in the absence of the bender, thus increasing the light intensity emitted and raising the light beam produced compared with the light beam produced by a conventional dipped beam.
A second example embodiment of a headlight device for performing a motorway function is shown schematically in FIG. 2. A projection of the light beam produced by such a headlight device is shown in FIG. 3. In FIG. 2, a headlight device P comprises a first optical module M1 and a second optical module M2. Optical module means here an optical system comprising at least one light source, possibly disposed in a reflector, and possibly associated with one or more dioptric elements of the lens type; the light source can for example be implemented by one or more light emitting diodes grouped together, or by a halogen or xenon lamp in a reflector; the optical system in question is preferably self-contained, that is to say able to be switched on or off separately from the other modules of the headlight.
In this example, the first module M1 is for example able to perform the conventional dipped function; it therefore reproduces the previously described cutoff line 101. The first module M1 can also be a dual-function dipped/main-beam module. The second module M2 is a complementary module; for example, the second module can comprise one or more light emitting diodes, or LEDs, and a lens providing an at least partially flat cutoff line; in other example embodiments, other light sources than LEDs are used to produce the second module M2.
The activation of the second module M2, if it occurred without the activation of the first module M1, would produce a light beam whose projection 300 would be roughly rectangular or trapezoidal in shape, slightly below the horizon line 104; the projection angle observed between the horizon line and a higher line 301 of the light projection 300 is typically −0.34 degrees. The activation of the second module M2 combined with the activation of the first module M1 therefore generates a light beam whose overall shape is similar to that of a dipped beam, but with a cutoff line 302, shown in bold in FIG. 3, raised at least on the left hand part of the road, and whose light intensity is increased, compared with the light intensity of a dipped beam, close to the cutoff line of the global beam produced. Such a global beam can therefore be used to perform the motorway function.
Other examples of headlight devices for producing a beam of the motorway type exist in the prior art, for example multifunction headlight devices that comprise a light source and a movable cover selectively obscuring part of the light flux emitted by the source, thus making it possible to perform the dipped, main beam and motorway functions. In the invention, it will be possible to use any type of device able to produce at least one light beam of the conventional dipped type and a light beam of the motorway type; advantageously, the headlight devices used will be able to produce also light beams of the main-beam type.
For the general purpose of improving the driving comfort in terms of visibility, there exist, in the prior art, dual-function modules where the switching from dipped function to main beam function, and vice versa, is automatic, and the switching depending on the traffic conditions. With vehicles equipped with such dual-function modules, the presence of a vehicle liable to be dazzled by use of the main-beam function is sought. If no vehicle is detected, the main-beam function is automatically activated. As soon as the presence of a vehicle is detected, the main-beam function is automatically deactivated and the vehicle equipped with the dual-function headlight once again presents a light beam of the dipped type.
In practice, the threshold value as from which the absence of a vehicle detected allows switching to the main-beam function is fixed at 600 meters. As soon as a vehicle is detected at less than 600 meters from the equipped vehicle, it is the dipped function that is activated. However, this function provides fully satisfactory lighting only over a distance of around 60 to 80 meters. There therefore exist many traffic configurations, those in which the first vehicle liable to be dazzled is situated at more than 100 meters and at less than 600 meters from the equipped vehicle, for which the illumination of the road could be optimized without for all that dazzling the driver of any other vehicle.